The invention relates to a method of triggering a vehicle occupant restraint device. A sensor signal generated by a crash sensor is fed to a triggering device and to a clearing device supplying a clearing signal. The sensor signal is integrated in the clearing device and subjected to an examination.
A known method of this type is disclosed in British Patent document GB-2310303 A. The output signal of a single sensor is checked by various algorithms. If the one sensor supplies faulty signals, these should be recognized as being faulty. The method of operation of the clearing device is, therefore, dependent on the output signal. When the faulty signals have an appearance which is similar to that of signals which are typical of a crash, the differentiation is no longer possible. However, this may render the clearing device ineffective. A typical case of an output signal which cannot be recognized, or at least cannot be recognized with sufficient certainty, is that of a sensor with a “cold” soldered site. The latter has a slightly increased or fluctuating resistance. In the case of a method of operation which stresses the vehicle considerably, but is otherwise normal per se, the sensor generates signatures, which cannot be differentiated from a real crash.
It is an object of the invention to provide a method of triggering a vehicle occupant restraint device, in which a fuel sensor signal output by a crash sensor is fed to a triggering device and to a clearing device supplying a clearing signal, which has a secure and reliable method of operation of the clearing device.
The invention achieves this object by providing a method of triggering a vehicle occupant restraint device, in which a fuel sensor signal output by a crash sensor is fed to a triggering device and to a clearing device supplying a clearing signal, in which clearing device the sensor signal is integrated and subjected to an examination algorithm. The output signal of at least one additional crash sensor is also fed to the clearing device, in that the two output signals are linked to one another and are subsequently integrated during an observation period, and in that the clearing signal is generated when the integral exceeds a threshold value.
The method of operation of the clearing device is thus a function of at least one other crash sensor. Since it is highly probable that at least one sensor operates in a reliable manner, by means of this reference, a faulty second sensor can be reliably detected and it can be achieved that this fault is not exhibited in a faulty triggering of a restraint device.
Advantageous embodiments of the invention are described and claimed herein.
For triggering a vehicle occupant restraint system, such as an air bag, a belt tightening device, a rollover bar, etc., a clearing is required by use of a Safing algorithm. Input quantities include values ax(SFZ) and ay(SFZ) of an acceleration sensor in the vehicle center in the X and Y direction (X=direction of the longitudinal vehicle axis, Y=direction transversely thereto); also included are the values ax(SASL) and ax(SASR) of acceleration sensors in the A columns on the left (=L) and on the right (=R) and in the X direction as well as the values ay(SBSL) and ay(SBSR) of acceleration sensors in the B columns on the left and the right in the y direction. The sensors are not shown.
According to the invention, the (kinetic) energy input is computed in a clearing device which is also not shown. In this case, a differentiation is made between horizontal (=X) and lateral (=Y) energy. For the determination of the energy values, two integrals I are computed, once in the horizontal direction
      I    x    =            ∫              t        x            t        ⁢                  (                                            g              x                        ·                                          a                x                            ⁡                              (                SFZ                )                                              +                                    a              x                        ⁡                          (              SASL              )                                +                                    a              x                        ⁡                          (              SASR              )                                      )            ⁢              ⅆ        t            and once in the lateral direction
      I    y    =            ∫              t        y            t        ⁢                  (                                            g              y                        ·                                          a                y                            ⁡                              (                SFZ                )                                              +                                    a              y                        ⁡                          (              SASL              )                                +                                    a              y                        ⁡                          (              SASR              )                                      )            ⁢              ⅆ        t            
The weighting gx/gy is firmly parametrized and is used for the equalization of signal levels at the various positions in the vehicle center and at the A or B columns.
The computing of the integrals Ix,y starts at the point in time tx,y as soon as the amount of an acceleration value |ax,y| has in each case exceeded a defined threshold. The thresholds are clearly above the noise band and are not reached during the normal driving operation on an even road. When the acceleration values fall again and are all situated below their threshold values, the computing is terminated and the value of the integral is reset.
The integrals I are also reset when only one acceleration sensor exceeds its threshold value within a defined time window. The time window is initiated when the output signal of the acceleration sensor reaches the threshold value.